Microsoft fixes KB5089549 Windows security update install issues

Microsoft has resolved a known issue causing installation failures and 0x800f0922 errors when deploying the May 2026 Windows 11 security update (KB5089549). The problem, which has affected users for the past two weeks, stems from insufficient free space on the EFI System Partition (ESP), causing the update to automatically roll back on impacted devices.

When the installation failure occurs, users see a "Something didn't go as planned. Undoing changes." message during the reboot phase. Log entries show "SpaceCheck" and "ServicingBootFiles failed" indicators pointing to limited ESP free space. The issue is most pronounced on devices with 10 MB or less available on the EFI System Partition.

According to Microsoft, "On affected devices, the installation might proceed through the initial phases but fail during the reboot phase at approximately 35–36% completion." The problem was acknowledged two weeks ago, leaving IT administrators scrambling to update workstations without the critical May security patch.

Microsoft confirmed on Friday that the issue has been fixed in the Windows 11 KB5089573 preview cumulative update, released on May 26, 2026. This optional update includes 30 changes, encompassing performance and reliability improvements. The fix will be broadly available to all users who install the June Patch Tuesday updates later this month.

For organizations that cannot immediately deploy the preview update, Microsoft offers a workaround using Known Issue Rollback (KIR), a Windows feature that can reverse buggy updates pushed via Windows Update. Enterprise IT admins can manually mitigate the issue by installing and configuring a specific Group Policy, details of which are available on Microsoft's support website.

This is the second notable Windows update quality issue in recent months. Earlier in May, Microsoft confirmed that the April 2026 security updates were causing failures in third-party backup applications that relied on a vulnerable driver, and also fixed a Windows Autopatch bug that caused driver updates restricted by administrative policies to be deployed on some Autopatch-managed devices across the European Union.

Users are urged to install the KB5089573 preview update or wait for the June Patch Tuesday release to ensure their systems are both protected against security threats and reliably updated. The resolution of the ESP space issue underscores the importance of maintaining adequate partition sizes for critical system components.